The present invention relates to a network system in which a plurality of low-order networks, each having a plurality of nodes coupled via data paths, are mutually coupled by repeaters and data communication is performed between the nodes.
In a star network which uses a passive type optical star coupler as an optical distributor and executes data transmission between nodes by means of optical communication, it is inevitable that light attenuation is caused by the optical transmission path including the star coupler and the number of connectable nodes is limited. According to conventional network systems, therefore, network system expansion is realized by coupling a plurality of networks with optical repeaters that are each a relay device for system expansion.
FIG. 1 illustrates an example of a network system that has been expanded using such repeaters.
The network system comprises nodes N1 to N10, star couplers SC1 to SC5 and repeaters R1 to R4. A small or low-order star network is constituted around each of star couplers SC1-SC5, and a large or high-order star network is constituted around star coupler SC5. Repeaters R1-R4 are coupled between star coupler SC5 and the remaining star couplers SC1-SC4.
In the system illustrated in FIG. 1, if the high-order star network is a non-multiplexed or single-wavelength network, it can permit data communication only between a single pair of low-order star networks. For instance, data transfer from node N2 to node N5 is effected through star coupler SC1, repeater R1, star coupler SC5, repeater R2 and star coupler SC2 in the named sequence. During the data transfer the high-order star network is occupied by the task so that another data transfer, for example, from node N6 to node N9 is not possible. In this case, therefore, the data transfer from node N6 to node N9 becomes possible only upon completion of the data transfer from node N2 to node N5.